This application claims the benefit of Korean Application No. 2000-59840, filed Oct. 11, 2000, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to data modulation and correction methods, and more particularly, to a code modulation method for modulating data to be resistant to channel distortion and a method of correcting errors in detecting the data modulated by the modulation method.
2. Description of the Related Art
With the increased recording density of optical storage media, track pitches of digital versatile disc random access memories (DVD-RAMs), recordable DVD (DVD-R), or DVD rewritable (DVD-RW) become narrow. Accordingly, introduction of crosstalk or noise from neighbor tracks and the amount of inter-symbol interference (ISI) from neighbor pits are increasing. This disturbance increases jitter of a radio frequency (RF) signal, particularly when an optical storage medium whose physical address is recorded as pits are accessed.
Run length limited (RLL) codes having limited maximum and minimum constraints are common data modulation codes for optical storage media. A minimum run length, which is denoted by parameter xe2x80x9cd,xe2x80x9d greatly affects accuracy in detecting pits (or lands) in an optical disc and a recording density of an RLL code. The maximum run length, which is denoted by parameter xe2x80x9ck,xe2x80x9d is associated with code efficiency and code strategy. Common RLL codes also include consecutive run lengths between the minimum and maximum run lengths. For example, for eight-to-fourteen modulation plus (EFM+) codes compatible with the DVD family recording media, with d=2 and k=10, 1T (where T is a reproduction clock) spaced codes, excluding a sync code, exist at pit lengths 4T, 5T, . . . , and 10T between a minimum pit length of 3T and a maximum pit length of 11T. FIG. 1 is a histogram of the run length distribution of the EFM+codes. However, when jitter occurs in an RF signal being reproduced, due to any distortion in a channel, with the 1T spaced pits as shown in FIG. 1, a deviation of xc2x10.5T can increase the likelihood of data read error.
FIG. 2 is a table of a physical address format in a header field of a general DVD-RAM. For the general DVD-RAM, the same address data are written twice to the header field for high detection performance. The header field includes variable frequency oscillator (VFO1) data for a phase locked loop (PLL), address mark (AM) data, physical identification data (PID1), ID error detection data (IED1), and postamble data (PA1) for IED1 demodulation. To increase address detection, VFO2, AM, PID2, IED2, and PA2, which have the same functions as those above, are also written to the header field. However, even though address detection performance is improved, writing the physical address data based upon this RLL modulation code causes a redundancy problem.
To solve the above-described problems, it is an object of the present invention to provide a data modulation method modulating data to be resistant to channel disturbance/distortion, to provide a data modulation method increasing data detection performance, to provide a data modulation method reducing redundancies in the physical address sector (field) while maintaining improved address detection, and to provide a method of correcting errors occurring in reading the data written by a modulation method.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above objects and other objects of the present invention, there is provided a data modulation method to write data to an optical storage medium using an extended space run length limited (ES RLL) modulation code, the ES RLL modulation code being expressed as RLL (d, k, m, n, s) with s=2 or greater, where d is minimum run length, k is maximum run length, m is the data bit length before modulation, n is the codeword bit length after modulation, s is the space length between codewords, and using prescribed coding/modulation rules specifying run lengths as in+1=in+s (n=1, 2, . . . ).
It is preferable that, in the ES RLL modulation code, the run length is one of 2, 5, 8, and 11, the number of lead zeros of a codeword is one of 1, 4, and 7, and the number of end zeros of a codeword is one of 1 and 4.
It is preferable that the ES RLL modulation code is applied to write address data to a physical sector of the optical storage medium, the address data being required for data access.
It is preferable that the ES RLL modulation code is pre-formed as pits in the optical storage medium to write and store management information, for example, copyright information.
It is preferable that the data modulation method comprises discarding codewords modulated with the ES RLL modulation code that have a maximum run length to generate a read clock signal and a synchronization clock signal.
It is preferable that the data modulation method comprises discarding codewords modulated with the ES RLL modulation code that have a codeword digital sum (CDS) whose absolute value is relatively great, with preference of deleting the codewords having greatest CDS absolute value.
To achieve the above objects and other objects of the present invention, there is provided a data modulation method to write data to an optical storage medium using an extended space run length limited (ES RLL) modulation code, the ES RLL modulation code being expressed as ES RLL (d, k, m, n, s), where d is minimum run length, k is maximum run length, m is the data bit length before modulation, n is the codeword bit length after modulation, s is the space length between codewords, the data modulation method comprising, generating codewords satisfying an RLL (d, k, m, n, sxe2x89xa72) code, using coding rules specifying run lengths as in+1=in+s (n=1, 2, . . . ) and removing codewords having a maximum pit length from the generated codewords, and creating a codeword table of the remaining codewords, where T is a reproduction clock signal. In an embodiment, for example, the ES RLL code can be expressed as (2, 11, 8, 27, 3) and codewords having a maximum pit length of 12T be removed from the generated codewords.
The data modulation method further comprises, discarding from the codeword table codewords having a codeword digital sum (CDS) value whose absolute value is relatively great, and arranging the remaining codewords in ascending order of the absolute value of the CDS to reduce a direct current (DC) component of the codewords.
To achieve the above objects and other objects of the present invention, there is provided a data correction method to correct data read from an optical storage medium after the data has been written to the optical storage medium according to a run length limited (RLL) modulation code expressed as RLL (d, k, m, n, s), where d is minimum run length, k is maximum run length, m is the data bit length before modulation, n is the codeword bit length after modulation, and s is the space length between codewords, the correction method comprising, counting the run lengths of code sequences read from the optical storage medium by detecting bit transitions in the code sequences, and if an N-th pit that does not comply with prescribed RLL coding rules is detected, checking the run lengths of following M pits, and if the run length of any of the following M pits does not comply with the prescribed RLL coding rules, correcting the run length of the N-th pit according to the prescribed RLL coding rules.
The correction method further comprises, that if the run length of the N-th pit is s/2 less than a run length of the prescribed RLL code, correcting the N-th pit by adding s/2 to the run length of the N-th pit; and correcting the (N+1)th pit by subtracting s/2 from the run length of the (N+1)th pit.
The correction method further comprises, that if the run length of the N-th pit is s/2 greater than a run length of the prescribed RLL code, correcting the N-th pit by subtracting s/2 from the run length of the N-th pit; and correcting the (N+1)th pit by adding s/2 to the run length of the (N+1)th pit.
The data correction method above further comprises that, when using an ES RLL and s=3, if the run length of the N-th pit is 1 less than a run length of the ES RLL code, correcting the N-th pit by adding 1 to the run length of the N-th pit; and correcting the (N+1)th pit by subtracting 1 from the run length of the (N+1)th pit.
The data correction method above further comprises that when using an ES RLL and s=3, if the run length of the N-th pit is 1 greater than a run length of the ES RLL code, correcting the N-th pit by subtracting 1 from the run length of the N-th pit; and correcting the (N+1)th pit by adding 1 to the run length of the (N+1)th pit.
To achieve the above objects and other objects of the present invention, there is provided a data correction method to correct data read from an optical storage medium after the data has been written to the optical storage medium with an extended space run length limited (ES RLL) modulation code expressed as ES RLL (d, k, m, n, s) with sxe2x89xa72, where d is minimum run length, k is maximum run length, m is the data bit length before modulation, n is the codeword bit length after modulation, and s is the space length between codewords, the method comprising, counting the run lengths of code sequences read from the optical storage medium by detecting bit transitions, determining whether the counted run lengths comply with prescribed ES RLL modulation rules, where run lengths are expressed as in+1=in+s (n=1, 2, . . . ) with an initial run length of i1=d, and if an N-th pit which is not equal any of the run lengths in is detected, checking the run lengths of the following M pits; and (b) if the run length of at least one of the M pits is not equal to the run lengths in, correcting the run length of the N-th pit according to the prescribed ES RLL modulation rules. In an embodiment, the initial run length can, for example, be set to i1=1 or i1=2 if d=1 and d=2, respectively.
The correction method further comprises, correcting the run length of the N-th pit by adding a value to or subtracting a value from the run length of the N-th pit such that the run length of the N-th pit is equal to a run length in of the ES RLL that has an absolute value closest to the run length of the N-th pit, and correcting the run length of the (N+1)th pit by subtracting from or adding to the run length of the (N+1)th pit the value which is added or subtracted to the Nth pit. The value added or subtracted from the run length of the N-th pit can be based on whether a codeword after correcting the run length of the N-th pit would have a CDS having an absolute value closest to a CDS of a codeword before correcting the run length of the N-th pit, thereby maintaining absolute values of the CDS of codewords to be small.